These days a user can download an audiovisual document from a broadcaster to view it on his playback device. More recently, new miniaturized devices for playing back audiovisual transmissions have appeared on the market. Thus, personal digital assistants (PDAs) or even mobile telephones with color graphics screens, are provided with programs and memories for storing audiovisual documents, such as films, documentaries, sporting events, and so on. When the part of interest to a user concerns a small part of the image, the miniaturization of the screen makes it difficult for the user to follow the event.
Associating attributes with the image signals, whether digital or analogue, is widely practiced; these attributes typically concern the title, theme or even the display format. For example, the DVB-SI specification (Digital Video Broadcast—specification for Service Information) EN 300 468 V1.3.1 (published by the ETSI) specifies the attribute function and format associated with audiovisual documents. For example, an attribute specifies whether the video signals of the document are of 4/3 or 16/9 type. The playback device takes account of this attribute and adapts the display according to its value, which makes it possible to make maximum use of the screen area by distorting the image. However, in the case of devices with miniaturized screens, adapting the display to the screen size does not always make it possible to follow the event in satisfactory conditions.
The document U.S. 2004/148640—MASUKURA teaches a device for receiving from a network and playing back an audiovisual document on a screen. Attributes, called “Metadata”, are received from the network in association with the document, this metadata defining regions of the image that are to be enlarged so that they can be viewed more comfortably by the user. The transmission of such information occupies bandwidth and obliges the broadcaster to apply processing prior to transmission.